The test sleeps one second and expects the perf counter to
be one second or more. But in reality (probably esp. in VM
which I conducted my experiments), I mostly saw counters
between 0.9s - 1s and occasionally 0.8s - 0.9s.

So be a little bit conservative here when checking the
result.
Signed-off-by: Yonghong Song <yhs@fb.com>